This invention relates to the production of aluminum chloride and more particularly to the production of high purity aluminum chloride while minimizing chloride losses.
In the production of aluminum chloride suitable for subsequent electrolytic reduction to metallic aluminum by the chlorination of materials containing compounds of aluminum as well as other materials such as silicon, titanium, and iron, the resulting chlorides must be separated to provide a sufficiently high purity aluminum chloride for the subsequent electrolytic process to perform in a satisfactory manner. In King et al U.S. Pat. No. 3,786,135 there is disclosed and claimed a process for the recovery of high purity aluminum chloride from the gaseous effluent of chlorination of aluminum compounds which involves a first step of initially cooling the hot gaseous effluent sufficiently to selectively condense sodium aluminum chloride values therefrom and separating such initially condensed values as well as entrained particles from the gaseous effluent followed by a further cooling of the gaseous effluent to a second and lower predetermined temperature range to condense a high proportion of the remaining volatile constituents that are condensable above the condensation temperature of aluminum chloride. The final step claimed in that process relates to the direct desublimation of high purity aluminum chloride values in a fluidized bed of aluminum chloride at a temperature range of from about 30.degree.-100.degree. C. In this third or final step in the recovery of aluminum chloride, it is desirable to condense or desublime the aluminum chloride at as high a temperature as possible to inhibit concurrent desublimation or condensation of other metal chlorides such as titanium chloride, silicon chloride, or the like. Interrelated thereto is a particle size control which is also, under certain conditions, temperature-dependent. In patent application Ser. No. 765,458 entitled "Control of Purity and Particle Size in Production of Aluminum Chloride" there has been proposed a set of operating conditions which, in a single condenser or desublimation apparatus, seeks to control the purity of the product as well as the particle size while attempting to mitigate the chloride lossed by operating the condensing or desublimation apparatus at a temperature of about 60.degree.-80.degree. C. and controlling both the entrance velocity of the aluminum chloride gases and the overall throughput volume as well as by removing the particles of aluminum chloride from the bottom or adjacent the bottom of the condensation apparatus.